Ans:- When the
light ray passes from denser medium to air (or) vacuum, the angle of incidence
in the denser medium at which the angle in air (or) vacuum is 90o is
called critical angle of the denser medium Refractive
index of denser medium

2. What are the difference between
microscope and telescope?

Ans:-

Microscope

Telescope

1) It is used to see very
small objects.

1) It is used to see
distant objects.

2) Its objective is of
smaller focal length and of smaller
aperture.

2) Its objective is of
longer focal length and of larger aperture

3) Its eyepiece is of
longer focal length and of larger aperture

3) Its eyepiece is of
smaller focal length and of smaller aperture

4) It produces linear
magnification i.e., size of the image is larger than that of the object.

4) It produces linear
magnification i.e., size of the image is larger than that of the object.

Importance:- The element present in sun’s
atmosphere can be identified

4. Why do diamond’s sparkle?

Ans:-
Diamonds sparkle due to total Internal Reflection.

5. Define the magnetic momentum of a bar
magnet? What is its direction?

Ans:-
Magnetic moment:-It is defined
as the product of pole strength and magnetic length. It is represented by M

M =
m(2l)

It is
a vector its direction is always along south pole to north pole of the magnet

6. Do you find two magnetic field lines
intersecting? Why?

Ans:-
Two magnetic lines of force do not intersect with each other, Because if they
intersect, at the point of intersection the field should possess two different
directions which is impossible.

7. What is the magnetic moment of a semi
circular magnet of radius ‘r’ and pole strength ‘m’?

Ans:-
Magnetic moment is

M =
m(2r).

8. In the equal distance method of a
deflection magnetometer, the deflections produced by two bar magnets are 30o
and 60o. What is the ratio of their magnetic moments?

Ans:-

M1 :
M2 = 1:3

9. The electric lines of force do not
intersect why?

Ans:- They do not intersect if they intersect, at the
point of intersection intensity of electric field will act in two different
directions, which is not impossible.

10. Three capacitances , are connected in parallel (i) What is the ratio of charges?
(ii) What is the ratio of potential differences?

Ans:-
In parallel combination potential differences is constant where as charge changes.

Capacity

(i)

(ii) As potential is constant

11. Can there be electrical potential at
point with zero electric intensity?

Ans:-
Yes, electric potential is constant from the centre of a hallow spherical
conductor up to the surface and is equal to where as intensity of
electrical field is zero inside the conductor.

12. The potential earth is taken as zero? Explain?

Ans:-
Since earth is a huge conductor, an addition (or) removal of a small amount of
charge does not alter its electrical conduction. So its potential is taken as
zero.

13. What is the difference between electric
lines of force and magnetic lines of induction?

Ans:-
Electric lines of force are open loops where as magnetic lines of induction are
closed loops.

14. State Gauss’s law in electrostatics?

Ans:-
The total electric flux through any closed surface is equal to times the net charge
enclosed by the surface. Here is the permittivity of
free space.

15. Repulsion is the sure test of
electrification then attraction? Why?

Ans:-
A charged body may attract a neutral body and also an opposite charged body.
But it always repels a like charged body. Hence repulsion is the sure test of
electrification.

16. Write down the used of capacitors?

Ans:-
(i) To store electrical charges at low potential

(ii)
In tuning circuit of radio

(iii)
To produce strong electric fields in small space

(iv)
As filters to stop D.C and allow A.C

17. What are the ohmic and non-ohmic
devices?

Ans:-
Ohmic devices:- Devices that obey
ohm’s law are called ohmic devices

Ex:-
(i) All metallic conductors, at constant temperature.

Non-ohmic devices:-
Devices that does not obey ohm’s law are called

Non-ohmic devices

Ex:-
(ii) p-n junction diode, Thermistor.

18. The manganin wire is used in the
preparation of standard resistances. Why?

Ans:-
The temperature coefficient of resistance of manganin wire is very low. Hence
its resistance its resistance almost remains constant at different
temperatures. Hence it is used in the manufacture of standard resistance.

19. Write two differences between emf and
p.d ?

Ans:-

Emf

POTENTIAL DIFFERENCE

1) The difference of
potential between the terminals of a cell in open circuit is emf

1) The difference of
potential between the terminals of a cell in closed circuit is potential
difference (P.D)

2) A source of electric
current like a cell can have emf

2) Any part of a closed
circuit can have potential difference (P.D)

20. Which of the two, namely voltmeter and
potentiometer is preferable to measure the emf of a battery? Why?

Ans:-
Potentiometer is preferable to measure the emf of battery.

Voltmeter
draws current from battery, while measuring its emf. But potentiometer draws no
current from the battery, when potentiometer is balanced.

21. When is the series combination of cells
advantageous and why?

Ans:-
Series combination of cells is advantageous when more emf at low current is
required. In series combination of cells, Where r<<R. Then

i.e.,
Potential difference across the external resistance is n times emf of each
cell.

22. When is the parallel combination of
cells advantageous and why?

Ans:-
Parallel combination is advantageous when more current is to be drawn at low
potential.

In
parallel combination cells, In R<<r, Then

i.e.,
if external resistance is very small, current drawn is ‘n’ times that of a
single cell.

23. What is the internal resistance of a
cell? Write the value of internal resistance of an ideal cell?

Ans:-
The internal resistance of a cell is the resistance of the electrolyte between
the anode and cathode Internal resistance of an ideal cell is Zero

24. What is the specific resistance of
material of a conductor. Mention its units?

Ans:-
The resistivity of a material is numerically equal to the resistance of a
conductor of that material having one meter length and one square meter area of
cross section

Units:-ohm meter .

25. What is the force on a conductor of
length ‘l’ carrying current ‘i’ when it is situated in a magnetic field of
induction B? When is it maximum?

Ans:-
force on a current carrying conductor in a magnetic field

F
=

Force
is maximum when B and l are perpendicular to each other,

26. State Fleming’s left hand rule?

Ans:-
Fleming’s left hand rule:- Stretch the left hand such that the thumb, the
fore finger and central finger are mutually perpendicular to each other. If
fore finger indicates the direction of magnetic field of induction. The central
finger indicates the current in the conductor. And the direction of force on
the conductor is indicated by the thumb.

27. A moving coil Galvanometer can measure a
current of What is the resistance
of the shunt to measure 1A.

Ans:-
In the frequency range from a few MHz up to about 30 MHz, long distance
communication can be achieved back by ionosphere reflection of radio waves back
towards the earth. This mode of propagation is called sky wave propagation and
it is used by short wave broadcast services.

48. Define modulation. Why is it necessary?

Ans:-
The process of combining audio frequency signal with high frequency signal is
called modulation.

Need of modulation:To
separate audio frequency signal with millions of low frequency in the
atmosphere.

49. What is “World Wide Web” (W.W.W)?

Ans:-
It is an encyclopedia of knowledge accessible to every one round the clock
throughout the year.